This invention relates to logging carriages of the type typically used in logging operations on mountainous terrain.
Logging operations on mountainous terrain provide a challenge in retrieving the logs. Often it is not easy to drive a vehicle, even a tractor, to the location where a log has fallen. Techniques have been developed to recover such logs using cables strung between two masts. Typically the mast at one end is a tree and at the opposite end is part of a yarder which is a wheeled or treaded vehicle having the mast and winches for winding cables. A logging carriage traverses the cables between the two masts. A drop line extends downwardly from the carriage. Logs are connected to the drop line and are hoisted upwards towards the carriage. The carriage is then moved towards the yarder and dropped in a convenient location where they can be trucked away. Typical prior art carriages require some mechanism for lowering the drop line so it may be connected to logs which are subsequently lifted and carried away by the carriage. The drop line is actually just a downward extension of a generally horizontal main line extending from the mast of the yarder and connected to a winch on the yarder. The drop line typically extends about one or more sheaves within the carriage and then extends downwardly towards the ground. A mechanism can be provided for rotating the sheaves, but some device must be provided to ensure that the sheaves grip the drop line and carry it downwards towards the ground as the sheaves rotate.
For example, one type of carriage, known as the "Eagle Carriage", wraps the drop line over two vertically spaced-apart sheaves. A third sheave, connected to a hydraulic ram, squeezes the cable between the three sheaves. One of the sheaves at least is powered, often by a diesel engine. This pulls the cable downwardly as the sheaves rotate.
Often these devices are relatively heavy and expensive, particularly when they must accommodate a diesel engine and often a hydraulic pump as well. Furthermore, the devices for gripping the cables often are unreliable in operation.
Accordingly, it is an object of the invention to provide an improved gripping device for securing a cable, or other flexible, tension member, about a sheave or another such rotatable member, which is simple in construction and relatively light in weight.
It is also an object of the invention to provide a carriage capable of operating on different types of yarders and uphill or downhill terrain.
It is a further object of the invention to provide an improved gripping device which does not require an engine.